The present invention relates to a semiconductor integrated circuit device, and relates in particular to a supporting substrate construction appropriate for a high speed circuit.
In recent years, the development of compound semiconductor elements to carry out high speed logic operations in the field of semiconductor integrated circuits has become active. For example, an electric field effect transistor (FET) employing a GaAs semiconductor wafer, which carry out a high speed switching operation in approximately 100 psec, has been obtained. The integrated chip of the integrated circuit devices which carry out such high speed operation are composed within a conventional package. These devices have a problem in that high speed performance in the integrated circuit itself cannot be obtained. Various causes of the deterioration of high speed performance have been considered. One of these causes has been attributed a difficulty in matching termination of the high speed input signal to the circuit.
For example, in the case of the high speed input signal is launched into a FET of an input section within the GaAs integrated circuit through a transmission line, the high speed input signal is reflected almost completely, and interferes with the input signal because the input impedance of the FET is high. As a result, waveform distortion is occurred. Normally, to prevent this, termination using a matching resistor is carried out. FIG. 6a is an equivalent circuit of an example of a termination construction. A matching resistor 12, having the same value as the characteristic impedance of a transmission line 11, is arranged close to the input lead of a package 14. The package 14 normally includes a substrate, a semiconductor chip, wiring patterns and a lid for sealing. For example, in an ECL circuit employing a silicon substrate and having a switching speed of approximately 1 nsec, the problems caused by the reflection of input signal have been prevented by mounting the matching resistor on the outside of the package.
However, if the switching speed is approximately 100 psec, the wiring distance in FIG. 6a from point A of the package outside to the input terminal B of the integrated circuit chip 13 packed therein, becomes a serious problem. This wiring portion between A and B is called an open stub, and when it is increased in length, the actual input signal to the integrated circuit chip 13 is of a ringing waveform. As a result, the input signal causes a mis-operation of the chip 13. To prevent this, in principle, it should be enough to accommodate the matching resistor using a thick film printing technique or a chip resistor within the package as close to chip as possible.
However, it is difficult to form a resistor within a substrate having an uneven surface using the thick film printing technique. Further, a chip resistor occupies a considerably larger space within the package, which increases the size of the overall device.
FIG. 6b is an example of another termination construction. This is called "feed-through termination". In this construction, the input signal is launched to wiring pattern 15 on the substrate of the package 14 from the outer lead 11 through the input section of integrated circuit chip 13, and is terminated by the matching resistor 12. In this construction, there is no need to arrange the matching resistor close by the chip 13, and there is no problem if the wiring distance from the point A to the point C is long. However, in the abovementioned conventional construction, it is necessary two ports corresponding to the only one input signal.
As described above, as the matching termination method in the input section of the integrated circuit of high speed operation, the method to take the termination on the front of the chip causes the problems of the open stub, and feed-through termination requires two ports.